This invention relates to the technical sector of synthetic agents characterized by flocculating and/or coagulating action.
The invention relates specifically to the technical sector of synthesis and applications of polyvinylamines (PVA).
In particular, the invention relates to applications of such PVAs in manufacture of paper and especially for production of paper or cardboard sheets exhibiting an array of interesting properties.
The invention also relates to application of PVAs in the water treatment industry and to the area of petroleum and parapetroleum activities.
The invention also relates to all known applications of flocculants and coagulants.
During manufacture of paper, cardboard, or the like, or in preparation of fluids for petroleum or parapetroleum use, or in treatment of waste water, specifically xe2x80x9cmunicipalxe2x80x9d waste water containing urban waste, use of flocculant and/or coagulant agents is well known, especially retention agents of the polymer type whose function it is to retain a maximum of fines and charges in a sheet of paper, or again flocculation/coagulation agents whose function it will be to flocculate waste suspended in waste water, etc.
In the area of paper the beneficial effects resulting from a retention agent are essentially:
increase in production and lowering of manufacturing costs: energy savings, smoother running of the machine, higher yield of fibers, fines, charges, and anionic upgrading products, lower acidity in the circuit combined with decreased use of aluminum sulfate and accordingly fewer corrosion problems;
improvement in quality: better formation and better look-through; improvement in moisture content of the sheet, opacity, breaker stack, absorptivity, and decrease in the porosity of paper.
Polymers were introduced as flocculants about forty years ago, with the molecular weights which were relatively low at the time. U.S. Pat. No. 3,235,490 (Goren) describes various gel polymers.
Certain Goren polymers have been used as coagulants, especially for the purpose of coagulating very fine solids in suspension.
The addition of bentonite to the paste was proposed long ago; it may be added to other mineral products such aluminum sulfates, even synthetic polymers, in particular polyethylene imine (see, for example, documents DE-A-2 262 90s and U.S. Pat. No. 2,368,635).
Document U.S. Pat. No. 3,052,595 proposed combination of bentonite with a polyacrylamide with an essentially linear characteristic. This process was found to compete with systems easier to apply while being characterized by performance just as high. In addition, even with the current linear polyacrylamides, the retaining power is still insufficient.
Document EP-A-0 017 353 proposes combination of a non-ionic to slightly anionic copolyacrylamide with bentonite for retention of low-charge pastes (maximum of 5% of charges). This process makes hardly any progress, since these polymers are relatively low-performing with respect to retention, in particular charged pastes, undoubtedly as a result of insufficient synergy between these polymers and bentonite, which has little tendency to recoagulate.
Document EP-A-0 235 893 proposes resort to cationic polyacrylamides of molecular weight higher than one million, thirty million or more, essentially linear polyacrylamides. In this way a retention effect is obtained which is certainly satisfactory but still deemed insufficient in application to paper, since bentonite entails difficulties during subsequent treatment of effluents at the machine outlet, and users select this system only if there are significant advantages.
In notes presented in connection with a course in Seattle, 11-13 October 1989, and published with the title xe2x80x9cSupercoagulation in the control of wet end chemistry by synthetic polymer and activated bentonite,xe2x80x9d R. Kajasvirta described the mechanism of supercoagulation of activated bentonite in the presence of a cationic copolyacrylamide, without specifying the exact nature of the mechanism. This process entails the same disadvantages as the one referred to in the preceding paragraph.
Lastly, EP 0 574 335 has disclosed an important improvement, use of branched polymers (polyacrylamides in particular) in powder form.
Also known in the prior art are systems of retention agents for manufacture of a sheet of paper, cardboard, or the like which consist of a combination of two retention agents, generally a primary retention agent and a secondary retention agent. What is involved in this instance is a system qualified as xe2x80x9cdual.xe2x80x9d
Patent U.S. Pat. No. 4,753,710 thus advocates use of a linear acrylic polymer of high molecular weight as primary retention agent which is added to the fibrous mass, then shearing, particularly in the mixing pump or xe2x80x9cfan pump,xe2x80x9d and then addition of bentonite (which is a swelling clay) as secondary retention agent.
In the area of waste water treatment there are, for example, patents EP 0 202 780 or EP 0 201 237, the teachings of which overlap. In this industry effort is applied to achieve clearness of water, an imperative for customer satisfaction, but also the greatest degree of dryness possible of the residue obtained and separated, since gain even of a minimal degree of dry content represents enormous savings in transportation of residues because of the smaller amount of water which has to be hauled.
Also of the state of the art among other polymers is polyethyleneimine or PEI, which is one of the oldest synthetic cationic flocculants. PEI is often used to treat industrial or municipal waste, but above all as draining and retention agent in the paper industry (the reference being to xe2x80x9cpolymin SKxe2x80x9d(trademark)).
Use of PVA or polyvinylamine, especially in the sphere of paper, has also been proposed in the prior art. PVA is known to form a structure of flakes both very solid and of small dimension, one including little bound moisture.
Patent BASF DE 44 09 903 describes a process of PVA synthesis which is applied at around 40xc2x0 C. and which yields a gel which is then dispersed in methanol. The polymerization system employs a pure azoic catalyst; no redox system is in operation in accordance with the technique described. In addition, the process is very slow and highly complex.
The patent Mitsubishi JP 07 118 333 discloses polymerization by precipitation based on solution in a solvent of the methanol type. The process is slow and complex because of the constraints associated with use and recirculation of a solvent.
Patent Mitsubishi GB 2 308 123 discloses a complex process of precipitation by PEG (polyethylene glycol) and hydrolysis of the solution obtained on the basis of the resulting product.
These two patents utilize pure azoics.
Also known is the patent Mitsui JP 0 628 7232, which also discloses use of an azoic catalyst.
Patent BETZ Canada 2110366 uniquely describes polymerization in solution with a pure azoic system and an application as coagulant.
Other documents (among others, GRACE) describe a bentonite paper application combined with a PVA and a polyacrylamide.
Patent BETZ U.S. Pat. No. 5,292,441 describes a process of PVA quaternization.
The patent BASF U.S. Pat. No. 5,290,880 describes a PVA synthesis which utilizes initiation of polymerization at 25-80xc2x0 C. by a complex redox system combined with an azoic catalyst, with heavy mechanical constraints such as mixture constraints with prepolymerization. All the examples include initiation which is conducted only with a pure azoic, at a temperature of the order of 60xc2x0 C. According to this document polymerization is carried out at a temperature which may reach 150xc2x0 C.
This patent is to be compared to patent U.S. Pat. No. 4,808,683, which claims polymerization at temperatures ranging from 30 to 100xc2x0 C., with examples around 60xc2x0, or again patent U.S. Pat. No. 4,421,602, which specifies polymerization by means of a complex redox initiator system combined with an azoic, with polymerization temperatures of 30 to 140xc2x0 C., with examples at 40, 50, and 60xc2x0 C.
There is also patent EP 0 220 603, which describes conduct of PVA synthesis in supercritical CO2.
As is to be seen, many industrial groups have made many attempts at using PVA, but use of PVA has until now been in conflict with the obligation of resorting to complex synthesis processes involving numerous stages and numerous intermediate products utilizing effects of pressure, temperature, vacuum, or mixing operations, presence of solvents, etc, and so expensive processes resulting in complex engineering entailing costly and difficult application also creating problems with respect to the environment such as created by use of solvents.
Hence the PVAs obtained require industrial application which is either difficult or costly or complex, or entails both disadvantages simultaneously.
Now PVA continues to be a very interesting product because of its high capacity for coagulation and even flocculation.
There has long been a clearly identified need of large industrial groups, but one not satisfied, for availability of a PVA which is easy to produce, as directly as possible by industrial means, by a simple process, while complying with current environmental impact standards, at low cost, one easy to be used in the industries in question. A simple process conducted at atmospheric pressure and at a low temperature would be especially highly appreciated, for obvious reasons.
An attempt has always been made to work at a low temperature, without success, for reasons other than economic, especially because of the low reactivity of the monomer NVF (N-vinylformamide), and also because the expert knows that, if polymerization is initiated and conducted at a low temperature, the molecular weight of the PVA obtained will be higher, because of better control of polymerization, which is a recognized need in these industries.
It is of course essential that these improvements not be made to the detriment of the properties of the agent and contemplated flocculation and/or coagulation applications, the complexity and often antagonistic character of which, well known to the expert, were referred to earlier.
Hence one object of the invention is to develop such a process which is simple, direct, inexpensive, and which leads directly to a PPVA product usable in a simple and direct application process despite the known low and discouraging reactivity of NVF.
It is claimed for this invention that use is made of a PVA (polyvinylamine) type polymer obtained by a special synthesis process as coagulation/flocculation agent designed to effect clear-cut improvement in the retention, formation, draining, and other properties of a sheet of paper or cardboard thereby obtained, or the flocculation/coagulation of streams of industrial or municipal effluents, and waste water in general.
The PVA may be obtained either as a unique agent or one mixed with other known flocculation/coagulation agents.
The invention relates to a process of synthesis at low temperature and under normal or atmospheric pressure of polymers such as PVA (polyvinylamine), in powder form or in emulsion, on the basis of the monomer N-vinylformamide.
The word xe2x80x9cpolymersxe2x80x9d is used here and throughout the patent application to designate both homopolymers and copolymers with monomers copolymerizable with N-vinylformamide, nonrestrictive examples of which being acrylamide or substituted derivatives of acrylamide, (meth)acrylic acid, the (meth) acrylates, the esters of (meth) acrylates, the monomers known by the abbreviations APTAC, MAPTAC, AMPS, n-vinylacetate, acrylonitrile, and DADMAC.
Note: APTAC=acrylamidopropyltrimethyl ammonium (chloride) MAPTAC=meth(APTAC) DADMAC=diallyldimethylammonium (chloride)
As a first option, the polymerization claimed for the invention is a polymerization in bulk, in an aqueous medium or in water, at a temperature which may be as low as xe2x88x922xc2x0 C. or 0xc2x0 C. or 2xc2x0 C., maximum +5xc2x0 C. to 10xc2x0 C., is initiated by an original combination of redox and azoic catalyst(s), then continues at a temperature below 100xc2x0 C., and is conducted under more or less normal or even, preferably, atmospheric pressure.
Polymerization is conducted in water and results in a non-ionic PVA polymer gel.
It is followed by direct hydrolysis with the gel obtained at the end of polymerization in order to obtain a cationic PVA polymer which is subjected to a standard drying stage, for example, in a fluidized bed or in a rotary oven.
In this way there is obtained directly a dry cationic PVA in powdered form, of high molecular weight, directly applicable in industry, a PVA which allows highly interesting applications in the industries referred to.
The powder may be used as such or may be dissolved in an aqueous medium such as water, and the agent claimed for the invention may be used alone or in combination with other powders and/or other solutions of known flocculant agents and/or coagulants, in a compatible physical form.
In the prior art mentioned above polymerizations were always carried out at a temperature very substantially higher than 0xc2x0 C. and even substantially higher than ambient temperature, such as 50, 60, 70xc2x0 C., or even 100xc2x0 C. Most often the polymerization was also carried out under pressure. Even patent BASF U.S. Pat. No. 5,290,880, which in the opinion of the applicant represents the proximate state of the art, in the sense that it describes a combination of azoic and redox initiator, but citing only a pure azoic, azobisamidopropane dichlorohydrate, in his ten examples (something which separates the expert from the redox/azoic solution), is forced to initiate polymerization between 25 and 80xc2x0 C., in particular around 60xc2x0 C. in the examples, and to conduct the polymerization at a high temperature, of the order of 150xc2x0 C.
Moreover, in the prior art cited, one succeeds in obtaining only PVAs in liquid or emulsion form or in the form of a product reprecipitated or dried by drying by pulverization or xe2x80x9cspray-drying,xe2x80x9d something which entailed the well-known disadvantages such as the necessity of transporting large amounts of water and solvent, the necessity of reversing the emulsion at the location at which it was used, and the like. At best it was possible to precipitate an acetone powder on the basis of PVA in emulsion, but this represents an additional step, and so significant added industrial cost, a step which entails use of acetone, a dangerous solvent which must be recycled, again at significant added cost.
According to the invention, in contrast, a directly usable dry powder is obtained immediately, a powder of great interest to the industries in question.
As a second option, which will be described below, the polymerization may also be conducted in an emulsion while being initiated at a low temperature of the order of 15 to 20-25xc2x0 C.
It is claimed for the invention that use may also be made to advantage of the xe2x80x9cdry powderxe2x80x9d which may be obtained by drying the emulsion in question, in particular by drying by pulverization (xe2x80x9cspray-dryingxe2x80x9d) or by densification drying. A xe2x80x9cdry powderxe2x80x9d such as this presents advantages in terms of molecular weight and flocculation capacity.